According to a rotary electric machine in which a stator is formed in a fractional slot configuration, noise and vibration generated when the rotary electric machine is driven generally tends to increase as compared to a rotary electric machine in which a stator is formed in an integral slot configuration. JP2010-075049A which is hereinafter referred to as Reference 1, JP2003-032983A which is hereinafter referred to as Reference 2 and JP2002-165428A which is hereinafter referred to as Reference 3 are examples each of which includes an object to decrease noise and vibration generated at the time of driving of the rotary electric machine.
According to a rotary electric machine disclosed in Reference 1 where a stator includes the fractional slot configuration, the number of slots of the stator and the number of poles of a rotor are specified by a predetermined relational expression. Then, the rotary electric machine in Reference 1 obtains a combination of the number of stator poles and the number of rotor poles. In addition, the rotary electric machine in Reference 1 also attempts to reduce torque ripple of the rotary electric machine in the same way. The aforementioned conditions are also applied to rotary electric machines disclosed in References 2 and 3.
According to the rotary electric machines disclosed in References 1 to 3, the combination of the number of stator poles and the number of rotor poles is limited. As a result, in the rotary electric machine including a wide range of drive rotation numbers, it may be impossible to choose an appropriate combination of the number of stator poles and the number of rotor poles, which may inhibit noise, vibration and torque ripple, for example, generated at the driving of the rotary electric machine from decreasing.
A need thus exists for a rotary electric machine which is not susceptible to the drawback mentioned above.